1. Field of the Invention
The present invention relates to liquid crystal display device, and more particularly, to a liquid crystal display device, which prevents driving circuit malfunction by preventing the introduction of impurities generated by friction induced by a screw coupling the liquid crystal display device, and by preventing damage to an inner wire caused by the screw.
2. Description of the Related Art
High quality visual display of electronic information has become crucial in the global information-based economy. Demand has increased for displays that have low power consumption characteristic, that are thin and light, and that have high picture quality. To meet this demand, liquid crystal display devices have been developed that have the advantages of sharp image quality, low power consumption, and are thin and light compared to other displays.
The structure of a related art liquid crystal display device is described below. The liquid crystal display device includes a liquid crystal display panel formed by bonding a thin film transistor array substrate and a color filter substrate with a predetermined cell gap between them, and disposing a liquid crystal layer between the bonded thin film transistor array substrate and color filter substrate. The liquid crystal display device further includes a driving unit for driving the liquid crystal display panel and a backlight unit for emitting light to the liquid crystal display panel.
The thin film transistor array substrate includes a plurality of gate lines and a plurality of data lines that define a plurality of regions, which are arranged vertically and horizontally on the substrate, defining a plurality of pixels. These pixels are arranged in a matrix fashion on the thin film transistor array substrate.
At the color filter substrate, red, green and blue color filter layers are formed corresponding to each pixel, and a black matrix surrounding the peripheries of the color filter layers is formed to prevent leakage of light from the color filter layers and prevent color interference of light passing through the pixels.
A common electrode and a pixel electrode are respectively formed on the color filter substrate and the thin film transistor array substrate, which apply an electric field to the liquid crystal layer by a voltage difference between the two electrodes. A pixel electrode is provided in each pixel, which enables display of an image by controlling the light transmittance of each individual pixel.
Accordingly, a liquid crystal display device displays an image by controlling the amount of light passing through the liquid crystal layer. Light is generally provided by a backlight unit disposed adjacent to the liquid crystal display panel. The backlight unit includes a lamp for emitting light and an inverter for supplying power to the lamp. The lamp is arranged on the side or rear of the liquid crystal display panel.
Liquid crystal display devices have been developed with panels having different surface areas according to purpose and place of use. For example, small liquid crystal displays have been developed for applications including small home appliances, navigation devices, and digital video displays. Despite the small size, the liquid crystal display panel provided therein is designed to have as large surface area as possible. In such applications, the distance between the periphery of the liquid crystal display device and the edge of the liquid crystal display panel becomes considerably smaller and thus, the space becomes narrower. This configuration is referred to as a narrow bezel design.
Further, to reduce the thickness of a small liquid crystal display device, an edge type backlight unit is used, which supplies light to a liquid crystal display panel by arranging a lamp on the side of the liquid crystal display panel. U-shaped or L-shaped lamps are common examples. Such an edge type backlight unit is described below.
FIG. 1 illustrates a related art edge type backlight unit. Referring to FIG. 1, the edge type backlight unit includes a L-shaped lamp 20 bent along the periphery of a liquid crystal display panel, and a plurality of lamp wires 15 and 16 for supplying power applied through a connector 10 to opposite ends of the lamp 20.
A high voltage is needed to drive the lamp 20. Though not shown in the drawings, the liquid crystal display device includes an inverter for supplying high voltage to the lamp 20. The inverter converts an external direct current voltage into an alternating current of high voltage to supply it to the lamp 20. A voltage applied through the connector 10 is applied to the anode of the lamp 20 via the lamp wires 15 and 16. High voltage lamp wire 16 and low voltage lamp wire 15 are each arranged in a narrow space between the periphery of the liquid crystal display device and the liquid crystal display panel.
The arrangement of the lamp wires 15 and 16 and the structure of the liquid crystal display device as described below.
FIG. 2 is an exemplary view illustrating a cross section of the liquid crystal display device. Referring to FIG. 2, the liquid crystal display device includes a light guide plate 135 for uniformly dispersing light from a lamp (not shown) and supplying it to upper portion of the liquid crystal display device; a reflective plate 136 for reflecting the light irradiated onto a lower portion of the light guide plate 135 toward the upper portion; and an optical sheet 137 for concentrating and dispersing the light emitting through the light guide plate 135 and supplying it to upper portions. The liquid crystal display device further includes a liquid crystal display panel 130 for displaying an image by controlling the transmittance of light through the optical sheet 137; polarizing plates 132 attached to both surfaces of the liquid crystal display panel 130 for polarizing light; a bottom cover 140 provided under the reflective plate for protecting the reflective plate 136 and the light guide plate 135; a guide panel 145 for protecting the side of the bottom cover 140 and an upper portion of the light guide plate 135; and a top case 150 for pressing and fixing the liquid crystal display panel 130 provided on the light guide plate 135 and for coupling to the side of the guide panel 145.
The liquid crystal display panel 130 is formed by bonding a thin film transistor array substrate 130b and a color filter substrate 130a, with the polarizing plates 132 being disposed on both surfaces of the liquid crystal display panel 130.
The light guide plate 135, reflective plate 136 and optical sheet 137 are arranged within the space formed by coupling the guide panel 145 and the bottom cover 140. The light guide plate 135, reflective plate 136 and optical sheet 137 are sequentially laminated to supply light from the lamp evenly and stably to the entire surface of the liquid crystal display panel 130. Though not shown, the lamp is arranged on the side of the light guide plate 135, on the opposite side of a lamp wire 117 to supply light to the light guide plate 135.
The lamp wire 117 for supplying power to the lamp is arranged in the space between the bottom cover 140 and the light guide plate 135. However, there is no particular structure for preventing movement by fixing the lamp wire 117 in the space between the bottom cover 140 and the light guide plate 135. The top case 150, the guide panel 145, and the bottom cover are coupled into a single unit by a fastener, such as a screw.
FIG. 3 is an exemplary view illustrating the liquid crystal display device coupled by a screw. FIG. 3 is substantially similar to FIG. 2 except that a screw 260 is additionally shown. Referring to FIG. 3, a screw 260 passes through top case 150, guide panel 145, and bottom cover 140 through the side of the top case 150. The forward part of the screw 260 penetrates the space between the bottom cover 140 and the light guide plate 135. Accordingly, the top case 150, the guide panel 145 and the bottom cover 140 are fastened by screw 260.
However, liquid crystal display devices with a narrow bezel design have a considerably narrower space between the bottom cover 140 and the light guide plate 135 due to the fact that they have as large surface area of a liquid crystal display panel as possible. Therefore, the screw 260 passing through the top case 150, the guide panel 145 and the bottom cover 140 occupies a considerable area of the space between the bottom cover 140 and the light guide plate 135. Accordingly, a problem may occur where that a lamp wire 117 moving between the bottom cover 140 and the light guide plate 135 is damaged by the screw 260 coming through the bottom cover 140, and the coating of the lamp wire 117 is stripped, thereby exposing the interior wire. In this case, the exposed wire may make contact with the metal screw 260, thereby changing the voltage level supplied through the lamp wire 117. This changed voltage level may affect the amount of light emitted from the lamp, thereby degrading the picture quality of the liquid crystal display device.
Further, the screw 260 continuously causes friction with the top case 150, the guide panel 145 and the bottom cover 140 while passing through each of these components, which leads to the production of impurities caused by the friction. Since the top case 150, the guide panel 145, and the bottom cover 140 include pressed material made of metal, and the screw 260 is also made of metal, the impurities produced by the friction between them may cause degraded performance if they are introduced into a driving circuit for driving the liquid crystal display panel 131.